Conventional angioplasty has been preformed for several decades, prolonging the lives of an ever increasing number of patients. Angioplasty procedures involves the dilatation of a balloon placed across a lesion in a coronary artery. Dilatation of the balloon in turn dilates the lesion, opening the artery for increased blood flow. In some cases, however, the goal of the angioplasty procedure is, in whole or in part, frustrated by complete or partial reclosure of the artery at the lesion. Two mechanisms are believed to be principally responsible for reclosure of the artery, these are restenosis and recoil. Restenosis is believed to be caused by continued growth or regrowth of the smooth muscle cells associated with the lesion. Recoil is in part a mechanical process involving elastic rebound of the dilated lesion.
Several means have been disclosed for addressing the problem of restenosis. These include, among others, radiation treatments to slow or prevent smooth muscle cell proliferation associated with the restenotic process. Certain drug therapies have been proposed to prevent or slow restenosis.
Several means have also been developed to address the issue of recoil. One of the more significant developments in this area has been stents, which can be permanently deployed to mechanically hold open lesions. Although stents have been found to be highly effective, they may irritate the wall of a artery in which they are implanted. Some believe that this may encourage limited restenosis. Warming of the lesion during dilatation has also been disclosed to prevent or slow recoil. Warming the lesion is believed to soften the lesions such that it may be "remodeled" that is, thinned under low pressure. Heating of the lesion, however, is believed to cause an injury response which may cause some restenosis.